[asan] Pass -falign-functions=16 when building on Windows #154694
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Win/ASan relies on the runtime's functions being 16-byte aligned so it can intercept them with hotpatching. This used to be true (but not guaranteed) until llvm#149444. Pass the flag to explicitly request enough alignment.
llvmbot
added
compiler-rt
compiler-rt:asan
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@llvm/pr-subscribers-compiler-rt-sanitizer Author: Hans Wennborg (zmodem) ChangesWin/ASan relies on the runtime's functions being 16-byte aligned so it can intercept them with hotpatching. This used to be true (but not guaranteed) until #149444. Pass the flag to explicitly request enough alignment. Full diff: https://github.com/llvm/llvm-project/pull/154694.diff 1 Files Affected:
diff --git a/compiler-rt/lib/asan/CMakeLists.txt b/compiler-rt/lib/asan/CMakeLists.txt
index d1d229e3e6d40..3850d3ce8a9d7 100644
--- a/compiler-rt/lib/asan/CMakeLists.txt
+++ b/compiler-rt/lib/asan/CMakeLists.txt
@@ -106,6 +106,14 @@ if(MSVC)
endif()
set(ASAN_CFLAGS ${SANITIZER_COMMON_CFLAGS})
+# Win/ASan relies on the runtime having 16-byte aligned functions for
+# hotpatching. See https://github.com/llvm/llvm-project/pull/149444
+if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+ if(CMAKE_CXX_SIMULATE_ID MATCHES "MSVC")
+ list(APPEND ASAN_CFLAGS /clang:-falign-functions=16)
+ endif()
+endif()
+
append_list_if(MSVC /Zl ASAN_CFLAGS)
set(ASAN_COMMON_DEFINITIONS "")
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thurstond
approved these changes
Aug 21, 2025
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This will only work if the function following
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I think it would work in practice, but |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/169/builds/14280 Here is the relevant piece of the build log for the reference |
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Win/ASan relies on the runtime's functions being 16-byte aligned so it can intercept them with hotpatching. This used to be true (but not guaranteed) until #149444.
Pass the flag to explicitly request enough alignment.